Injector of compact design for a common rail injection system for internal combustion engines

ABSTRACT

A common rail injector is proposed which is very compact in structure and nevertheless brings high closing forces to bear at the end of the injection. This is attained, among other provisions, in that the closing piston has a larger diameter than the nozzle needle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 35 USC 371 application of PCT/DE00/02825 filed onAug. 18, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an injector for a common rail injection systemfor internal combustion engines, having a valve control chamber, definedby the end face of a nozzle needle, in which the fuel inlet takes placevia an inlet throttle and the fuel outlet takes place via an outflow Cthrottle, and there is a closing piston in the valve control chamber.

2. Description of the Prior Art

To reduce the structural length of conventional injectors, variousefforts have been made, with the goal of X constructing injectors inwhich the nozzle needle discharges N directly into the valve controlchamber, and no valve piston is necessary. From European Patent 0 426205, an injector is known in which the nozzle needle discharges directlyinto the valve control chamber. Located in the valve control chamber area control element and a closing piston. A disadvantage of this design isthat the closing piston and the control element with an inlet throttleand outflow throttle are disposed in line with one another, so thatdespite the omission of the valve piston, the structural length of theinjector is still comparatively great. Furthermore, the closing forcesat the end of injection are relatively slight.

SUMMARY OF THE INVENTION

The object of the invention is to furnish an injector that is especiallycompact in structure and simple in design, and in which the closingforces at the end of injection are high.

According to the invention, this object is attained by an injector for acommon rail injection system for internal combustion engines, having avalve control chamber, defined by the end face of a nozzle needle, inwhich the fuel inlet takes place via an inlet throttle and the fueloutlet takes place via an outflow throttle, and there is a closingpiston, which has a greater diameter than the nozzle needle, in thevalve control chamber.

This injector has the advantage that its structural length is especiallyshort, since there is only one closing piston in the valve controlchamber. Furthermore, in the injector of the invention the closing forceat the end of injection is especially high, because the diameter of theclosing piston is greater than the diameter of the nozzle needle.Finally, by reducing the number of components of the injector, a simpledesign of the injector has been achieved.

A variant of the injector of the invention provides that the closingpiston is disposed between the inlet throttle and outflow throttle onone side and the nozzle needle on the other, so that the closing pistonalso takes on control tasks.

In another embodiment, it is provided that the closing piston has afirst bore, extending between its end faces, so that the positivedisplacement work which the nozzle needle must perform upon opening ofthe injection nozzle counter to the pressure in the valve controlchamber is slight.

In an advantageous feature of the invention, the closing piston has athrottle bore extending between its end faces, so that after the end ofinjection, the closing piston can be returned to its outset position ata defined speed.

In a supplement to the invention, a stroke stop is provided in the valvecontrol chamber and limits the displaceability of the closing piston inthe direction of the inlet throttle and the outflow throttle, so thatthe fuel can flow unhindered into and out of this portion of the valvecontrol chamber.

In a further version, a closing spring is present, which is bracedagainst the closing piston and the nozzle needle, so that after the endof injection the closing piston is moved into its outset position by thespring force.

In an advantageous feature, it is provided that the closing spring isdisposed in the valve control chamber, so that a simple design isassured, and the spring force acts directly on the closing piston.

In a supplement to the invention, it is provided that the closing springis braced against the end face of the nozzle needle, so that the nozzleneedle is simple in design.

Another variant provides that the nozzle needle has a pin protruding inthe direction of its longitudinal axis and past its end face, so thatthe portion of the valve control chamber defined by the closing pistonand the end face of the nozzle needle does not fail to attain a minimumvolume predetermined by the length of the pin. Because of the elasticityof the fuel, this minimum volume brings about a certain elasticity or“softness” of the injector in the valve control chamber and the walls ofthe valve control chamber.

In another variant of the invention, the first bore of the closingpiston is closable by the pin, so that with the the injection nozzleopen, the pressure in the valve control chamber between the closingpiston and the nozzle needle drops no more than necessary, and theleakage losses between the nozzle needle and the valve control chamberare reduced.

In a supplement to the invention, it is provided that the first bore ofthe closing piston has a sealing seat on the face end toward the nozzleneedle, and the pin has a corresponding sealing cone, so that especiallygood sealing between the pin and the closing piston is achieved.

A variant provides that the inlet throttle and/or the outflow throttleis disposed in a housing of the injector, so that the dimensions of theinjector are reduced still further.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages and advantageous features of the invention can belearned from the ensuing description, taken with the drawings, in which:

FIG. 1 is a cross section through an injector according to theinvention; and

FIG. 2 is an enlarged detail X of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, an injector according to the invention is shown. Via ahigh-pressure connection stub 1, fuel 3 is carried via an inlet conduit5 to an injection nozzle 7 and via an inlet throttle 9 into a valvecontrol chamber 11. The valve control chamber 11 communicates with afuel return 17 via an outflow throttle 13, which can be opened by amagnet valve 15. The fuel 3 is shown in FIG. 1 as a black area.

The valve control chamber 11 is defined by a nozzle needle 21. Thenozzle needle 21 prevents the fuel 3, which is under pressure, fromflowing into the combustion chamber, not shown, between injections. Thisis achieved by the provision that the nozzle needle 21 is pressed into anozzle needle seat 22 and seals off the inlet conduit 5 from thecombustion chamber, not shown.

The nozzle needle 21 has a cross-sectional change 23 from a largerdiameter 25 to a smaller diameter 27. The nozzle needle 21 is guidedwith its larger diameter 25 in a housing 29. The cross-sectional change23 defines a pressure chamber 31 of the injection nozzle 7.

In FIG. 2, an enlarged detail X of FIG. 1 of the injector of theinvention is shown. In this view it can be seen that the valve controlchamber 11 is defined by an end face 33 of the nozzle needle 21. Aclosing piston 34 is located in the valve control chamber 11 and has afirst, larger bore 35 and a second, smaller throttle bore 36. The strokeof the closing piston 34 in the direction of the magnet valve 15 islimited by a stroke stop 37. A pin 38 with a conical tip that fits intoa complimentary sealing seat 39 of the closing piston 34 protrudes fromthe end face 33 of the nozzle needle 21. FIG. 2 shows a state of theinjector in which the closing piston 34 rests on the stroke stop 37, andthe nozzle needle is seated on its nozzle needle seat 22, not shown inFIG. 2. In this position, there is a gap between the pin 38 and thesealing seat 39 of the closing piston 34, so the fuel 3, not shown inFIG. 2, can flow through the first bore 35 of the closing piston 34 intothe part of the valve control chamber 11 located between the closingpiston 34 and the nozzle needle 21.

When the outflow throttle 13 is closed, the hydraulic force acting onthe end face 33 of the nozzle needle 21 is greater than the hydraulicforce acting the cross-sectional change 23, because the end face 33 ofthe nozzle needle 21 is larger than the annular face of the area of thecross-sectional change 23. If the high-pressure pump, not shown, of thefuel injection system is not driven because the engine is at a stop,then a closing spring 40, acting on the end face 33 of the nozzle needle21, presses the nozzle needle 21 against the nozzle needle seat 22 shownin FIG. 1 and thus closes the injection nozzle 7 or injector.

When the outflow throttle 13 is opened, which happens when a ball 41 ofthe magnet valve 15, not described in detail, is lifted from a ball seat42, the pressure in the valve control chamber 11 drops. As aconsequence, the hydraulic force acting on the end face 33 drops aswell. As soon as this hydraulic force is less than the hydraulic forceacting on the cross-sectional change area 23, the nozzle needle 21 movesin the direction of the closing piston 34, until the pin 38 rests on thesealing seat 39. As a result, the injection nozzle 7 shown in FIG. 1 isopened, and the fuel 3 is injected into the combustion chamber. Theopening travel of the nozzle needle 21 is represented in FIG. 2 by thenozzle needle stroke “h”.

The inlet throttle 9 prevents a complete pressure equalization betweenthe inlet conduit 5 and the valve control chamber 11. The opening speedof the nozzle needle 21 is determined by the difference in flow betweenthe inlet throttle 9 and the outflow throttle 13.

This indirect triggering of the nozzle needle 21 via a hydraulic forcebooster system is necessary, because the forces required for rapidopening of the nozzle needle 21 cannot be generated directly with themagnet valve 15. The so-called “control quantity” required in additionto the fuel quantity injected into the combustion chamber reaches thefuel return 17 via the inlet throttle 9, the valve control chamber 11,and the outflow throttle 13. In addition to the control quantity,leakage also occurs at the nozzle needle guide. The control and leakagequantities can amount to up to 50 mm³ per stroke. They are returned tothe fuel tank, not shown, via the magnet valve 15.

To terminate the injection, the outflow throttle 13 is closed by theball 41 of the magnet valve 15, in a known manner not explained infurther detail. As a result of the closure of the outflow throttle 13,virtually the same rail pressure builds up again via the inlet throttle9 in a portion 43 of the valve control chamber 11 that is defined by theclosing piston 34 and the outflow throttle 13. This pressure exerts ahydraulic force on the nozzle needle 21 via the end face 45 of theclosing piston 34 and via the pin 38 resting on the sealing seat 39. Assoon as this hydraulic force exceeds the hydraulic force acting on thecross-sectional change area 23, the nozzle needle 21 closes. Because theend face 45 of the closing piston is markedly larger in comparison tothe annular face area of the cross-sectional change 23, the closingmotion takes place very fast and with great force. Simultaneously withthe closing motion, a small portion of the fuel, flowing into theportion 43 of the valve control chamber 11, flows through the throttlebore 36 into the valve control chamber 11 defined by the closing piston34 and by the end face 33 of the nozzle needle 21. The closing motiontakes place so fast that before a pressure equalization is reached, thenozzle needle 21 rests on the nozzle needle seat 22 again, and theinjection is terminated. The closing speed of the nozzle needle 21 isdetermined essentially by the flow through the inlet throttle 9.

In order for the closing piston 34 to move to the outset positionagainst the stroke stop 37 after the end of injection, the portion ofthe valve control chamber 11 defined by the closing piston 34 and theend face 33 of the nozzle needle 21 is filled with fuel through thethrottle bore 36, while the closing spring 40 presses the closing piston34 upward. It is also conceivable to omit the throttle bore 36 and todimension the play of the closing piston 34 in the housing 29 in such away that the fuel flows through the annular gap between the closingpiston 34 and the housing 29. The second end face 47 of the closingpiston 34 can also, as shown in FIG. 2, have a shoulder, which servesfor instance to guide the closing spring 40.

The foregoing relates to a preferred exemplary embodiment of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

1. In an injector for a common rail injection system for internalcombustion engines, having a valve control chamber (11) defined at oneend by the end face (33) of a nozzle needle (21), in which the fuelinlet to the control chamber takes place via an inlet throttle (9) andthe fuel outlet takes place via an outflow throttle (13), and there is aclosing piston (34) in the valve control chamber (11), the improvementwherein the closing piston (34) has a larger diameter than the nozzleneedle (21) and wherein the closing piston (34) has a first bore (35),extending between its end faces (45, 47).
 2. The injector of claim 1,wherein the closing piston (34) is disposed between the inlet throttle(9) and outflow throttle (13) on one side and the nozzle needle (21) onthe other.
 3. The injector of claim 2, wherein the closing piston (34)has a throttle bore (36) extending between its end faces (45, 47). 4.The injector of claim 2, wherein that a stroke stop (37) is provided inthe valve control chamber (11) and limits the displaceability of theclosing piston (34) in the direction of the inlet throttle (9) and theoutflow throttle (13).
 5. The injector of claim 2, wherein a closingspring (40) is present, which is braced against the closing piston (34)and the nozzle needle (21).
 6. The invention defined in claim 5, whereinsaid closing piston (34) has a first bore (35) and a throttle bore (36)extending between its end faces (45, 47).
 7. The injector of claim 6,wherein that the closing spring (40) is disposed in the valve controlchamber (11).
 8. The injector of claim 2, wherein the nozzle needle (21)has a pin (38) protruding in the direction of its longitudinal axis andpast its end face (33).
 9. The injector of claim 1, wherein the closingpiston (34) has a throttle bore (36) extending between its end faces(45, 47).
 10. The injector of claim 1, wherein that a stroke stop (37)is provided in the valve control chamber (11) and limits thedisplaceability of the closing piston (34) in the direction of the inletthrottle (9) and the outflow throttle (13).
 11. The injector of claim 1,wherein a closing spring (40) is present, which is braced against theclosing piston (34) and the nozzle needle (21).
 12. The injector ofclaim 1, wherein that the closing spring (40) is disposed in the valvecontrol chamber (11).
 13. The injector of claim 12, wherein the closingspring (40) is braced against the end face (33) of the nozzle needle(21).
 14. The injector of claim 11, wherein the closing spring (40) isbraced against the end face (33) of the nozzle needle (21).
 15. Theinjector of claim 1, wherein the nozzle needle (21) has a pin (38)protruding in the direction of its longitudinal axis and past its endface (33).
 16. The injector of claim 15, wherein the first bore (35) ofthe closing piston (34) is closable by the pin (38).
 17. The injector ofclaim 16, wherein the first bore (35) of the closing piston (34) has asealing seat (39) on the face end toward the nozzle needle (21), and thepin (38) has a corresponding sealing cone.
 18. The injector of claim 1,wherein the inlet throttle (9) and/or the outflow throttle (13) isdisposed in a housing (29) of the injector.